Just click on your ticker and it should take you back to the website, pop in your password (mine actually holds the password I think) and your details that you have previously put in should be there. Just change your weight and the date and you are done. It will change in the forum automatically.

Are you using The Ticker Factory? If so when you first make your ticker it advises you to bookmark the final page, or to save a particular URL. As far as I can tell each user gets a unique URL where they can alter their data. It will save your password automatically (or at least it did with mine) so it's just a matter of remembering the page.

If you've lost your URL you may have to make a new ticker. Just make sure to bookmark the page once you're done.